1. Field of the Invention
The invention is concerned with articles manifesting a variation in compressability for adapting to unequal loading. Articles of particular significance are mattresses, cushions, etc., for supporting or partially supporting the human body. Articles of interest are produced from continuous sections of a yieldable material, such as, foamed plastic or rubber.
2. Description of the Prior Art
The preemptive position once enjoyed by conventional fibrous particulate materials, sometimes incorporating separate spring elements, has long since yielded to modern technology. For many purposes, manufacture is dominated by moldings of continuous material, such as, natural rubber or synthetic polymers. It is common to increase compressability in such molded objects by foaming; and exemplary articles now marketed make use, for example, of foamed polyurethane.
By the time this new technological approach had been introduced, the earlier manufacturing techniques had reached a level of sophistication in which provision had already been made for unequal loading. So, for example, mattresses of the "inner spring" variety had been popularly marketed. Such structures permit regions of greater loading to yield to a lesser extent than and in a manner more or less independent of adjacent regions of lesser loading. Designers of molded counterparts early recognized the desirability of tailoring yield, and many approaches have been used. A prevalent approach depends on incorporation of foaming agents which produce gas bubbles and, therefore, local expansion. Another approach involves a variation in distribution of such foaming agents or, alternatively, a variation in activation of such agents, to result in unequal expansion--therefore, in tailored density resulting in the desired variation in compressibility. Another alternative which may be considered as involving a density variation on a massive scale makes use of spiked molds which result in surface craters, generally of even spacing but sometimes of varying spacing, so as both to increase and sometimes tailor compressibility. Particularly where large voids are introduced, this approach is necessarily practiced on a non-supporting surface.
Increased compressibility may be accomplished by producing voids by other means; and known articles have been produced by use of continuous slots, sometimes intersecting. While slotting has commonly been discussed as an alternative approach to reducing effective density, it has sometimes been considered analogous to the use of independently acting, separately inserted springs. Analogous to such prior art construction, slotting has been of uniform depth and spacing so as to produce uniform, individual yield characteristics.